1. Field of the Invention
The present invention relates to ink circulation in an image forming apparatus using an inkjet head.
2. Description of the Related Art
Conventionally, in an inkjet printer or the like using an inkjet head, a system of supplying circulated ink to the inkjet head is used as a recovery measure to eliminate bubbles and foreign matter from around an ink ejection port of the head. This circulation system is described in JP-A-2006-289955 and so on. Also, a mechanism to circulate ink for the purpose of eliminating bubbles from a tube is described in JP-A-11-192717.
However, in the system of JP-A-2006-289955, since ink is directly pressurized by a pump, modification and cavitation tend to occur in the ink. There is also a problem that the modified ink returns to the inkjet head and causes the image to be unstable. Meanwhile, in the system of JP-A-11-192717, ink cannot be circulated during printing. Therefore, there is a problem that bubbles cannot be eliminated from the inkjet head once they have been generated in or have entered the inkjet head.